Photographic wastes are known to contain considerable quantities of silver. It is known to recover this silver by means of electrolytic processes such as described in U.S. Pat. Nos. 3,936,363; 3,985,634; 4,039,407; 4,108,658; and 4,126,465. All of these electrolytic methods have certain disadvantages which do not allow them to be used widely at a sufficiently low price to make the recovery of the silver in photographic waste economically worthwhile. The main disadvantage is the necessity of using considerable electrical energy. In addition it is necessary to provide a complex power supply to operate such an electrolytic system, thereby making a very expensive installation, both as regards first costs and operating costs. Furthermore making all of the silver plate out on the electrode is fairly difficult, particularly since it is necessary to reduce to a minimum the generation of hydrogen at the cathode. Furthermore the silver that is thus recovered is normally contaminated by the material of the electrode which is normally of iron. Thus it is normally necessary to further refine the silver thus produced before it can be used for applications requiring silver of a high degree of purity.
It is also known to recover silver from photographic waste by nonelectrolytic systems. Such systems, as seen in U.S. Pat. No. 3,996,046, employ physical-chemical reactions. The main disadvantage of those systems is that they normally also produce silver which is contaminated by other metals, albeit these other metals might also be noble. It is necessary to employ a solubilizing agent such as a metal capable of metathetic interchange with the silver sulfate and not with the other sulfates present in the solution. Thus the metathetic interchange must take place under extremely carefully controlled circumstances so as to obtain the maximum possible quantity of silver ions in the interchanging solubilizing agent. The process is therefore relatively complex and difficult to control, and even so it only produces silver nitrates.